1. Field of the Invention
This invention relates to a photovoltaic converter which can be used, for example, as a photodetector or a solar cell
2. Description of the Prior Art
Photovoltaic converters which have been previously suggested and put to practical use as, for example, photodetectors or solar cells make use of a p-n homojunction of a nonmagnetic semiconductor such as a p-n homojunction of Si, or a p-n heterojunction of two different nonmagnetic semiconductor such as a p-n heterojunction of p-type GaAs and n-type ZnSe. In these known photovoltaic converters, the long wavelength edges of their spectral photovoltaic responses have negative temperature coefficients corresponding to an electronic transition between the valence band and conduction band of the semiconductors used, or an electronic transition between the impurity level and the valence or conduction band of the semiconductors used. In other words, when the temperatures of the known photovoltaic converters decrease, the long wavelength edges of their spectral photovoltaic responses shift to shorter wavelengths. For example, in a photovoltaic converter utilizing a silicon p-n homojunction, the long wavelength edge of spectral photovoltaic response is 1.12 .mu.m at 300.degree. K. but 1.09 .mu.m at 100.degree. K. On the other hand, the spectral photovoltaic response of a photovoltaic converter utilizing a p-n heterojunction of p-type GaAs and n-type ZnSe has a long wavelength edge of 0.92 .mu.m at 300.degree. K. and 0.88 .mu.m at 100.degree. K. in its spectral photovoltaic response.
When the photovoltaic converter is used as, for example, a photodetector, it is desirably maintained at a relatively low temperature of, say, 100.degree. K..+-.30.degree. K. However, as the temperature of such a known photovoltaic converter decreases, the long wavelength edge of its spectral photovoltaic response shifts to a shorter wavelength. Thus, at such a relatively low temperature, the photovoltaic converter cannot respond, or has a markedly reduced sensitivity, to light of relatively long wavelengths such as infrared rays,